1. Field of the Invention
The invention relates to a condensation chamber cooling system, comprising a condensation chamber for a boiling water reactor and at least one heat exchanger arranged outside the condensation chamber.
2. Description of the Related Art
It is generally known that light water reactors are used for current generation. In this case, nuclear fuel, for example in the form of uranium fuel rods, generates heat in a reactor core in a nuclear fission and decay process. In any event, care must be taken, by a discharge of heat from the reactor core, to ensure that the latter remains within an uncritical temperature range. In light water reactors (pressurized and boiling water reactors), the reactive core is arranged inside a pressure vessel or containment. In pressurized water reactors, this forms, with a steam generator and with the supply and discharge lines, a closed system for the circulation of coolant, the actual core reactor cooling system. In a pressurized water reactor, when it is operating normally, the steam generator and the following steam turbine with its condenser serve for discharging the heat transmitted as a result of the contact of the coolant with the fuel elements. In boiling water reactors, the steam generators are dispensed with, that is to say the steam from the reactor is utilized directly for driving the steam turbines, the heat of the coolant thus being given off. A typical reactor power output amounts, for example, to 1.4 GW. However, even when a light water reactor has been run down completely, for example for maintenance purposes, it generates residual, post-decay heat for a lengthy period of time. If this is not discharged reliably, there may be an unacceptable rise in temperature of the reactor core, together with possible fuel element damage, amounting to core meltdown.
If, in a boiling water reactor, the reactor core is covered with water, sufficient cooling may be assumed. In boiling water reactors, the post-decay heat occurring after a shutdown is discharged as a result of the boiling of the water surrounding the fuel elements. By the water being evaporated, an effect of cooling the fuel elements, which corresponds to the respective evaporation energy, occurs. The steam which thus arises is blown off via safety valves into a water reservoir outside the pressure vessel or containment, into what is known as a condensation chamber, and condenses there. The pressure vessel water inventory lost by the steam being blown off into the condensation chamber is typically recirculated out of the condensation chamber back into the pressure vessel by means of active feed systems.
During condensation, that is to say during the transition of the gaseous steam into its liquid state, a respective energy output occurs which causes the water located in the condensation chamber to be heated. According to the prior art, therefore, active emergency and after-cooling systems are provided, by means of which cooling of the condensation chamber or of the water reservoir located in it and the transmission of heat to an external heat sink, for example a cooling tower, take place via corresponding heat exchangers and heat circuits.
What proves in this case to be a disadvantage is that cooling systems of this type for discharging the condensation heat introduced into the condensation chamber are of the active type, that is to say active components, such as, for example, circulating pumps for the cooling medium, require water. In spite of maximum safety measures and a redundant design of the respective cooling systems, the situation cannot be entirely ruled out where an active cooling circuit, for example after the failure of its circulating pump, is not available in the event of an accident.